Methods and means for coating paper by film coating

ABSTRACT

This invention relates to the field of paper coating, more in particular to means and methods for providing paper with at least one layer of pigment using film coating to obtain a well printable surface. Provided is a method for preparing coated paper comprising the steps of:
         a) providing a pigmented wet coating formulation comprising water, 2-20 parts of a binder and 100 parts of pigment, wherein at least 50% of the binder is highly branched starch (HBS) characterized by a molecular weight of between 0.5*10 5  and 1*10 6  Daltons and having a molecular branching degree of at least 6% and which is obtained by treatment of gelatinized starch or starch derivative with a glycogen branching enzyme (EC 2.4.1.18); and wherein at least 70% of the pigment is calcium carbonate; and   b) applying the pigmented wet coating formulation to paper by film coating and drying the coated paper.

This invention relates to the field of paper coating, more in particularto means and methods for providing paper with at least one layer ofpigment using film coating to obtain a well printable surface. Thisinvention also is directed to a coated paper comprising a paper and onthe paper an amount paper coating composition of the present inventionfrom which the water has been reduced or removed.

Surface characteristics of coated paper play a vital role in paper andprint quality. Today, paper products must be designed with optimumsurface properties to meet increasing performance requirements.Technological advances, including bigger and faster machines, requirenew, more cost-effective, and environmentally friendly coating methodsand products.

The actual coating process usually comprises two steps: (i) theapplication of the coating medium containing pigments and binder (alsoreferred to as “coating composition”) onto the paper or board and (ii)the metering of the coating medium to the desired quantity (or coatweight). If the metering is done directly on the paper afterapplication, the process is called direct coating or (puddle) bladecoating. If, however, metering is done before the transfer of thecoating medium to the paper or board, the process is called indirectcoating or film coating. The present invention relates solely to meansand methods for indirect/film coating.

In coating papers by film coating, a high solids content of the coatingis beneficial (Glittenberg D., Filmpressenstreichen—Was kann man vonSpezialstärken erwarten. Wochenblatt für Papierfabrikation, 2009,(18-19), p.: 856-862). The maximum solids of a coating composition isdetermined by the dry solids of the ingredients used to prepare thecoating composition. The maximum solid content of the coatingcomposition on the film coater is limited by the maximum solids in whichthe starch solution can be prepared, the stability of the starchsolution and the rheology of the coating composition.

Immobilisation of the coating layer during application with the filmcoater is also important for the runnability. Immobilisation during thefilm coating process is influenced by the water retention capacity ofthe coating composition: on the one hand if the water retention is toolow, the coating film will run dry during application; on the other handif the water retention is too high the wet film layer will be too thickwith misting as a result. This requires a balanced water retention ofthe coating composition, which is strongly determined by the bindersystem, especially starch binders. Starches known to the person skilledin the art for use in the preparation of coating compositions increasethe water retention of the coating compositions, especially at high drysolids, thereby slowing down the immobilisation speed and creating moremisting. At increasing speeds, misting increases significantly,especially when applying more than 50% starch as binder. Speciallydeveloped synthetic polymers have been added to reduce the mistingtendency (Glittenberg D., Becker A., Voigt A., Kramm A., Van den AbbeeleH. Elimination of Misting during high speed metered size press coatingof starch containing coating colours with a new hyper-branched polymer,Professional paper making 2006, 2, p.: 50-55). However, disadvantage ofsuch polymers is the fact that they are oil based synthetics and addcosts to the coating composition.

In order to obtain a high dry solids coating for film coating operation,a starch solution with high dry solids is required. The maximum solidsof a starch solution is largely determined by the origin of the starch.In film coating application, partially depolymerised starches are beingused as coating binder. Conventional depolymerisation methods for starchare oxidation, dextrination or enzymatic conversion with alpha-amylase.In an enzymatic conversion process, a starch slurry of native starch isdegraded with alpha-amylase during the dissolution process. The maximumsolids content is limited to 30-35% due to the slurry concentration andthe high peak viscosity during dissolution. Moreover, starch solutionsof enzymatically degraded starch can easily show retrogradation andtherefore are less suitable for coating applications. Oxidised starchesand dextrins are cook-up starches. These types of starches can bedissolved to 35%-45% maximum dry solids. In this way, coatingcompositions with higher dry solids can be achieved. Moreover, thesetypes of starches are more visco-stable and are therefore generallyapplied in as binder in pigmented coating applications for the filmcoater. The maximum dry solids are determined by the starch slurryconcentration in which the products can be suspended prior todissolution. In general this is up to 40% for potato starch and up to45% for cereal starches. However, these types of starches are dissolvedin either a batch cooking or jet cooking process. Generally, live steamis used to cook the starch solutions which introduces condensation waterwhich is unwanted because it reduces the maximum dry solids of the finalstarch solution with 3% to 4%. The amount of cook-up starch that can beused as binder is limited because a) the starch solution dilutes thecoating composition too much, resulting in low dry solids and henceincreased misting, and b) when the quantity of starch in the bindercomposition increases, runnability problems occur due to increasingdilitancy, resulting in too high coating weights and misting.

One possible way to circumvent the disadvantage of dilution is to usecold water soluble starches which can be added directly to the coatingcomposition or which require a minimum of water to be dissolved.However, currently supplied cold water soluble starches are accompaniedwith several disadvantages. Commercially available low viscous coldwater soluble starches such as malto-dextrins have too low bindingpower. Another range of cold water soluble starches are cold watersoluble dextrins, such as yellow dextrins. However, these areaccompanied with disadvantages in the film coating operation and paperproperties: solubility in cold water is not 100%, the water retention istoo high which gives misting and the yellow composition of the starchdue to the dextrination process has a negative influence on thewhiteness of the paper. A commercial example of a (partially) cold watersoluble starch which may be used as coating binder in film coatingapplication is C*Icoat, supplied by Cargill.

Therefore, there is a clear need for starches which can be used asbinder in coating compositions for use in film coating, and which do notshow above mentioned disadvantages, thus yielding coating compositionswith excellent runnability, balanced water retention and, afterapplication, excellent paper properties.

More specifically, the present inventors aimed at the provision ofimproved means and methods for film coating of paper using starch as thepredominant binder. They particularly set out to identify a cold watersoluble starch or a starch which can be added dry, or which requires aminimum amount of water to be dissolved, or which can be used as aliquid with dry solids content of 50% or higher, which can be used asbinder in pigmented film coating formulations, while improving therunnability of the formulation. Ideally, the starch product should havea viscosity in solution lower than 1000 mPas, preferably lower than 800mPas measured with a Brookfield LVF at 50° C. and 50% dry solids (w/w).Preferably, the starch can be used in combination with other binderssuch as latex.

Surprisingly, it was found that the objective of the invention can beachieved with a starch that has been gelatinized and then converted tohighly branched starch using with a branching enzyme (E.C. 2.4.1.18) incombination with calcium carbonate as pigment.

Accordingly, in one embodiment the invention provides a method forpreparing coated paper comprising the steps of:

a) providing a pigmented wet coating formulation comprising 2-20 partsof a binder and 100 parts of pigment, wherein at least 50% of the binderis highly branched starch (HBS) characterized by a molecular weight ofbetween 0.5*10⁵ and 1*10⁶ Daltons and having a molecular branchingdegree of at least 6% and which is obtained by treatment of starch or astarch derivative with a glycogen branching enzyme (EC 2.4.1.18); andwherein at least 70% of the pigment is calcium carbonate; and

b) applying the pigmented wet coating formulation to paper by filmcoating, and drying the coated paper.

It was found that the unique combination of HBS as binder and calciumcarbonate as pigment allows for the use of the starch derivative at asolids content higher than or equal to 50%, providing a stable solutionwith low viscosity and having sufficient binding power. The coatingformulation has excellent runnability on the film coater while notshowing film splitting nor misting.

Good results were obtained using about 10-20 parts of binder wherein HBSwas combined with latex. In one embodiment, at least 50% of the totalbinder is HBS, preferably at least 55%, 60%, 65%, more preferably atleast 70% of the binder is HBS, most preferably at least 80%, like atleast 81, 83, 85, 86, 90%. In another aspect, HBS is the sole bindersince starch is relatively cheap, more sustainable and renewable.

The degree of molecular branching as used herein refers to the relativeamount of α-1,6 glycosidic linkages over the total of α-1,6 and α-1,4glycosidic linkages ((α-1,6/(α-1,6+α-1,4)*100%) and can be determined bymethods known in the art, e.g. using a combination of reducing enddetermination/isoamylolysis (Palomo M et al. 2009 Appl. Environm.Microbiology, 75, 1355-1362; Thiemann, V. et al, 2006 Appl. Microb. andBiotechn. 72: 60-71) and measuring the total amount of carbohydratepresent via the Anthrone/sulphuric acid method (see e.g. Fales, F. 1951J. Biol. Chem. 193: 113-124).

EP 2172489 relates to methods and means for providing altered starchcomprising treating starch with a branching enzyme of microbial origin,having improved resistance to retrogradation. However, it is completelysilent about the use of microbially altered starch for the manufacturingof paper or as binder in paper coatings.

The use of branched starch in an aqueous coating liquid is disclosed inthe art. EP0690170B2 describes a process for surface-sizing and/orcoating paper. Example 2 of EP060170B2 describes a coating compositionconsisting of 100 parts by weight of SPS as pigment and 12.5 parts byweight of branched starch as sole binder in a coating formulation fordirect coating using a puddle blade. This is distinct from the presentinvention describing the advantageous properties of HBS combined withcalcium carbonate as pigment for use in indirect or film coating. As isshown herein below, a coating composition comprising the composition ofExample 2 prepared according to EP060170B2 gives a poor runnability onthe film coater.

WO2007/103517 discloses paper coating compositions which contain water,a binder, a high viscosity hydroxyethylcellulose polymer and a pigment,wherein the pigment comprises greater than about 80% by weight calciumcarbonate pigment. Exemplary binders include those binders which arecommonly used in the paper coating arts, e.g. protein, starch, styrenebutadiene latex, styrene acrylate, polyvinyl acetate, and polyvinylalcohol. WO2007/103517 does not teach or suggest using highly branchedstarch. The coating compositions of WO2007/103517 were specificallydeveloped for use in blade coating methods, wherein high water retentionvalues are preferred. It does not show or suggest that the coatingcompositions have good runnability on the film coater, showing good filmsplitting and low misting tendency.

Moreover, WO2007/103517 does not define the binder system. In theexamples, the coating colours are devoid of starch or contain less than50% starch.

In step a) of a method according to the present invention, a pigmentedwet coating formulation comprising 2-20 parts of a binder and 100 partsof pigment is provided, wherein at least 50% of the binder is HBS havinga molecular branching degree of at least 6% and which is obtained bytreatment of starch or starch derivatives with a glycogen branchingenzyme.

Normal starch is composed of two constituents, the virtually linearamylose having alpha,1-4 glycosidic linkages and the alpha,1-6 branchedamylopectin. There are also variants of starch with almost exclusivelyamylopectin (waxy) or containing a high amylose amount. BE are enzymescapable of converting the alpha,1-4 glycosidic linkages present inamylopectin and amylose to alpha,1-6 bonds, thereby creating new branchpoints. When incubated with gelatinized starch the amylose and/or longside chains of the amylopectin are transferred to amylopectin with thecreation of new alpha,1-6 glycosidic linkages. This results to ashortening of the average side chain length and a significant reductionof the interaction capacity of the branched molecules. The resultingstarch derivative (herein referred to as HBS) has an average molecularweight (Mw) ranging between 0.5*10⁵ g/mol and 1*10⁶ g/mol, preferablybetween 0.8*10⁵ g/mol and 1.8*10⁵ g/mol, more preferably between 1*10⁵g/mol and 1.6*10⁵ g/mol. The HBS typically has an average molecularweight (Mw) of about 1.2*10⁵ g/mol. Molecular mass can be determinedusing different techniques, known to the person skilled in the art. Themolecular weight of the HBS of the invention was determined byGPC-MALLS-RI from Wyatt, USA equipped with a multiangle light scatteringinstrument (DAWN EOS) and an online viscometer (Viscostar). Refractiveindex was determined with RI2000 (Schambeck, Germany). The following setof columns was used: as guard column PwXL (Viscotek, USA) and aschromatography columns arranged in series: G4000PwXL and G5000PwXL(Viscotek, USA). A mixture of 50 mM NaNO3 and 0.1 M NaCl and azide wasused as running solution. The samples were solubilised in the buffer(mentioned above, 1 mg/ml) and filtered against 0.45 um before injectioninto the system. 0.2 ml was injected. Flow rate was 0.400 mL/min.Accuracy of the system was verified using dextrin standards (50K, 200K,400K and 800K).

The HBS of the invention has no measurable reducing power/DE.

Moreover, the HBS for use in the present invention has no residualamylose content. The amylose content is suitably measured according tothe KI/12 test. Solutions of starches that contain amylose will colourblue after addition of an aqueous mixture of KI and 12 due to theformation of a complex between amylose and iodine. A solution of amylosefree, amylopectin starch will colour purple although of lower intensity,due a different iodine-amylopectin complex. HBS starches from theinvention, however, do not give any colouration upon addition of theKI/12 aqueous solution, showing the absence of any amylose oramylopectin like structures.

WO 00/66633 discloses branched glucose soluble polymers and a method forthe production thereof. The branched starches from WO 00/66633 can bedivided into two sub-families: one family characterized by molecularweights between 1*10⁵ and 1*10⁶ Daltons, between 2.5% and 5% branchingand less than 1% reducing sugars, and a second family characterized bymolecular weights between 1*10⁷ and 1*10⁸ Daltons, between 5% and 10%branching and more than 6% reducing sugars. In contrast, HBS for use inthe present invention is characterized by molecular weights between0.5*10⁵ and 1*10⁶ Daltons, at least 6% branching and typically containsless than 1% reducing sugars. WO 00/66633 furthermore fails to teach orsuggest that branched starch can be used as binder in coatingcompositions.

US 2010/0058953 discloses a leguminous starch derivative for thepreparation of a paper or folding carton coating composition. The starchderivative is obtained by dextrination, leading not only to new α1->6bonds but also to α1->2 and α1->3 branching. US 2010/0058953 mentionsthat compositions with this type of starch have a propensity for mistingon a Film press, in particular at high speed, thus teaching away fromthe present invention. US 2010/0058953 does not define the bindersystem. In the examples, the binder system comprises a combination oflatex and leguminous starch derivative starch. Starch makes up only 23%to 38% of the binder system. The leguminous starch derivative of US2010/0058953 has an amylose content of less than 60%, preferably between25 and 55%. In contrast, the HBS according to the invention is typicallyamylose free.

The combination of calcium carbonate pigment and HBS as disclosed in thepresent invention combines a number of already known functionalproperties of BE modified starch (low viscosity at high concentrations,no retrogradation and a transparent solution) with some unexpectedfunctional properties (no film splitting, high binding power andbalanced water retention) that are highly beneficial for use in coatingsfor film coating application e.g. as a (partial) latex substitute. Inone aspect of the invention, HBS is the sole binder. Therefore, theinvention also provides a film coating method wherein the coatingformulation is devoid of latex.

As starting material for obtaining the abovementioned HBS anynative/unmodified starch derived from non-GMO as well as GMO plantvariants can be used, such as potato, corn, wheat, tapioca, waxy potato,waxy corn, waxy tapioca, high amylose potato, high amylose corn etc. Inaddition, modified starches are suitable including low DE maltodextrinsor amylomaltase-trated starch (e.g. Etenia), and chemically modifiedstarches. In one embodiment, the starch derivative is selected from thegroup consisting of the products of the enzymatic, chemical and physicalmodifications of starch of any type. For example, the starch derivativeis cationic starch, or oxidized starch, or phosphorylated starch.

The starch is first gelatinized before it can be brought into contactwith the BE. The starch is gelatinized in a batch or continuous processin a steam injection device (jet cooker). The gelatinized starch isbrought at the desired pH by the addition of acid or base and after thedesired temperature has been reached the BE is added and the solution iskept at the desired temperature for a desired period of time. Thus, theHBS is obtained from starch or starch derivative in completelygelatinized form.

Alternatively, the BE is added to a starch suspension at roomtemperature and while mixing the slurry is heated to the desiredtemperature and kept at that temperature for the desired period of time.The conversion conditions and the amount of enzyme added vary widelydepending on the starting material, the type of enzyme used and extentof the conversion. After the conversion has progressed to the desiredextent, the enzyme can be inactivated by increasing the temperature orby lowering the pH of the incubation mixture. This can then be followedby a filtration and ion exchange step to remove protein. Subsequently,the pH is adjusted to the desired pH and starch mixture is subjected todrying e.g spray drying, or evaporation, or reverted osmosis, or anothertechnique, to remove water and produce a high dry solid mixture.

The BE used can originate from any microbial source but preferably froma mesophilic or thermophilic microorganisms such as Aquifex aeolicus orRhodothermus obamensis. Accordingly, in one embodiment the glycogenbranching enzyme is a thermostable glycogen branching enzyme obtainedfrom a mesophilic or thermophilic organism, preferably glycogenbranching enzyme of Aquifex aeolicus or Rhodothermus obamensis.

Mixtures of HBS and other (starch-based) binders are also envisaged.Binders hold the pigment particles together, partially fill the voidsbetween the pigment particles and also bond the coating to the basesheet or precoating. Binders may be either natural or syntheticmaterials. Examples of natural organic binders include starch andproteins such as soy protein or casein. Examples of synthetic bindersinclude latices such as styrene-butadiene, vinyl acrylic copolymers, andpolyvinyl acetate and water soluble polymers such as Polyvinylalcoholand CMC. Protein and casein binders have high binding strength and formrelatively open coating structures. The limiting factor on use ofprotein binders is their high cost. They are normally used as cobindersin combination with latex. Styrene-butadiene (SBR) latices provideflexibility and hydrophobicity to the coating layer. Polyvinylalcohol isgenerally known as the binder with the highest binding power. However,price and dry solid content limit the amount that can be commerciallyand technically applied.

The invention is characterized in that HBS is used as binder togetherwith calcium carbonate as the major pigment. Pigments are minerals whichserve to provide optical and printability properties. White pigmentsprovide opacity to cover the dark surface of the paperboard andbrightness to obtain the desired degree of whiteness. High refractiveindex pigments such as titanium dioxide and calcined clay are veryeffective in scattering light and covering a dark surface of e.g.paperboard. Another key function of pigments is to control the degree ofink receptivity; this is dependent on the shape and size of pigmentparticles (morphology).

Preferably, at least 80% of the pigment is calcium carbonate, morepreferably at least 90% or 95%. Calcium carbonate pigments arecommercially available. Natural calcium carbonates are known genericallyas Ground Calcium Carbonate (GCC). In one embodiment, a method of theinvention uses an ultrafine ground calcium carbonate, e.g. sold underthe trademark Hydrocarb. In another embodiment, it is a PrecipitatedCalcium Carbonate (PCC) which is a synthetic calcium carbonate producedindustrially by means of a recarbonisation process. Different grades ofcalcium carbonate pigments of different particle size distribution andoptics can be used for coating applications. Preferably, at least 60%,like 70%, 75% or 80%, has a particle size of 2 μm or less. Suitablecommercial calcium carbonate pigments include Hydrocarb 75 and Covercarb75. Combinations of two or more types of calcium carbonates are alsoenvisaged.

Suitable other pigments for use in combination with calcium carbonateinclude clay and titanium dioxide, for example Capim DG. Using theproper combination of pigments controls the mean pore structure andsmoothness of the coated sheet surface. Some pigments, such as fineparticle size clay, are capable of being aligned to provide uniform lowangle reflectance of light upon calendering in an elastic nip; this ishow gloss is developed. Other pigments provide an open coating structurewhich can be the key to providing bulking and coating porosity; examplesof pigments with higher than average open area include calcium carbonateand calcined clay.

In step b) of a method of the invention, the pigmented wet coatingformulation is applied to paper by film coating and the coated paper isdried. Film coating methods and film coating apparatuses are known inthe art. In a film press, a film of the coating medium is formed andmetered on a large diameter roll. This roll forms a nip with anotherroll. The paper or board web passes this nip and picks up a certainportion of the film. Application can be—but does not have tobe—simultaneous on both sides. Metering is performed using meteringrods, which can be either smooth or profiled. Profiled rods provide acertain volume of coating medium due to the open cross section in theprofile. A deeper or coarser profile gives a higher coat weight than afine profile. The application weight is mainly adjusted by choosing anadequate profile. Typical coating weights range from about 8-11gsm/side. In one embodiment, the coating formulation is applied in atargeted amount of at least 6 gsm/side, preferably at least 7 gsm/side,more preferably at least 8 gsm/side, like 9, 10, 11 or 12 gsm/side.

Application may be done at any desired machine speed. As said, a coatingformulation of the invention shows very little misting even at highspeeds and high coat weights. Hence, machine speeds of at least 1100m/min, preferably 1200 m/min or more preferable at least 1300 m/min maybe used. For example, step b) comprises applying the coating formulationat a speed of at least 1200 m/min in an amount of at least 8 gsm/side.

Fine tuning of the application weight can be done by modifying the rodpressure. Profiled metering rods are mainly used for low viscosities (i.e. low solids contents of the coating medium) and low machine speeds.With increasing viscosity and speed, the rod loses contact with the rolldue to the hydrodynamic forces of the coating medium, comparable toaquaplaning. Then, the application weight depends less on the profileand more and more on the hydrodynamic conditions, such as rod pressure,rod diameter, viscosity and speed. Consequently, a smooth metering rodis often used. Typical rod diameters are 12-38 mm for smooth rods. Inone embodiment, a smooth rod having a diameter between about 20 and 30mm is used. Larger diameters yield higher application weights. Higherviscosities and machine speeds require smaller rod diameters for thesame application weight than lower ones. The coating medium is usuallynot transferred completely to the web. A certain amount remains on theroll and returns to the application unit where it is mixed with freshcoating medium. The transfer ratio depends on the acceptance behaviourof the web, on the properties of the coating medium and—to a limiteddegree—on the surface properties of the roll.

The pre-metered films usually have thicknesses of 7-20 μm (or ml/m²).Lower values would require very high rod pressures and also coverage ofthe web would be insufficient. Higher values are not meaningful sincethe web has a limitation with respect to coating acceptance. If theamount of pre-metered coating medium is too high, the surface of thecoated web appears uneven, with an “orange peel” character. At elevatedmachine speeds, the film split at the nip exit can create a fine mist ofcoating medium. This mist deposits on machine parts or even on the paperor board web. Since this misting increases with film thickness, it isthe major limitation for the application weight at high speed. Fortypical applications using prior art coating compositions, mistingbecomes a limitation above 1500 m/min.

It has been observed by the industry that paper coatings utilizinggreater than about 70% calcium carbonate by weight generally exhibits anundesirable rheological property of severe water loss from thesecoatings through absorption into the porous base sheet duringapplication. This severe water loss is a phenomenon that may also bedescribed as “poor water retention”. This poor water retention propertyis very problematic for the application of paper coatings containing100% GCC as a pigment, and even more severe of a problem with the use ofPCC as a pigment in paper coating compositions. Coating compositionswith poor water retention can run dry during film press operation due tostrong absorption of the liquid coating medium by the paper web. Thisresults in poor coverage and quality, and moreover to runnabilityproblems due to web brakes. Because of this poor water retentionproperty and associated runnability problems and in order to allowacceptable application of the wet coating to the porous base sheet, thecoated paper industry has been forced to utilize a relatively low solidscoating formulation, i.e. solids levels below 64% by weight, when 100%calcium carbonate is employed as a pigment. However, the drawbacks ofthe use of lower solids coating formulations creates two additionalsignificant problems: 1) the use of lower solids coating translates intohigher drying energy costs of the coated paper industry, and 2) lowersolids of coatings generally produces lower overall quality coatedpaper, since during the drying step when more water is employed in thecoating recipe, then more binder migration and coating shrinkage occursthereby affecting the finished coated paper quality negatively.

On the other hand, coating compositions with high water retention arealso associated with poor runnability on the film press. In case ofstrong water retention, the coating medium is not absorbed by the paperweb in the nip of the film press, which results in a poor transferratio. The film split after the nip then causes severe misting,especially at increasing speeds and coat weights.

Due to its unique properties, the use of HBS as a binder as disclosed inthe present invention allows to prepare wet coating formulations havinga solids content of at least 60% by weight, preferably at least 65%,like 66%, 67% or 68%, more preferably at least 70% by weight. The uniquecoating formulation disclosed in the present invention allows to achievecoat weights above 7 g m⁻² without misting at high machine speeds, like1800 m/min. The paper web can be dried according to conventionalmethods. Infra Red (IR) drying and Air drying can be employed to dry theweb after application of the liquid coating. Also drying cylinders maybe applied to dry the coated paper. Usually, the paper is dried to amoisture content of 4-6% for finished paper, or to 2-3% when the paperis prepared for post treatment with one or more coating layers.

After the paper has been coated, it may be treated with a calenderingstep to increase the gloss and smoothness of the paper. The purpose ofcalendering is to increase the gloss of the paper and improve theprintability. In a calendering device, the paper is run between two ormore rollers. By compression and heating of the rollers, the paper isgiven a more smooth surface and unevenness of the surface is reduced togive a glossy appearance and improve printability. Usually two types ofcalenders are employed to treat coated papers: soft nip calender andmulti nip calender. In a soft nip calender, the coated paper iscompressed in 1 to 4 nips of which at least one roller is covered withan elastic material. In a multi-nip calender employs 6 to 12 rollers,which are either covered with an elastic material, or heated. Both thesoft-nip calender as well as the multi-nip calender can be on-line oroff-line.

The invention also relates to film coating formulations and methods forpreparing the same. A paper coating composition of the present inventioncontains water, HBS as binder, and a pigment, wherein the pigmentcomprises greater than about 80% by weight calcium carbonate pigment.The pigment may comprise higher levels of calcium carbonate such asgreater than about 85% by weight calcium carbonate pigment, preferablygreater than about 90% by weight calcium carbonate pigment, morepreferably greater than about 95% by weight calcium carbonate pigment.The calcium carbonate pigment may be in the form of a ground calciumcarbonate or in the form of a precipitated calcium carbonate. The groundor precipitated calcium carbonate may comprise up to about 100% byweight of the pigment.

In one embodiment, a pigmented wet paper coating formulation compriseswater, 2-20 parts of a binder and 100 parts of pigment, wherein at least50% of the binder is highly branched starch (HBS) having a molecularbranching degree of at least 6% and which is obtained by treatment ofstarch or starch derivatives with a glycogen branching enzyme (EC2.4.1.18); and wherein at least 70% of the pigment is calcium carbonate.

In another embodiment, the pigmented paper coating composition has a drysolids content of at least 65% by weight, comprising at least 80% byweight calcium carbonate as its pigment component and a modified starchas binder, the modified starch being a highly branched starch (HBS)obtained by treatment of starch or starch derivatives with a glycogenbranching enzyme (EC 2.4.1.18) and having a molecular branching degreeof at least 6%.

Preferably, at least 70%, more preferably at least 80% of the binder isHBS. In one embodiment, HBS is the sole binder and/or calcium carbonateis the sole pigment.

Coating formulations are typically expressed in terms of dry parts, withthe total dry parts of pigment in a given formulation always equal to100. Other coating components are expressed in parts as a ratio to 100parts pigment. Additionally, thickeners and rheology modifiers areapplied to coating formulations to improve the runnability on machine.The type of thickeners or viscosifiers that can be applied are, but notlimited to, water soluble cellulosic derivatives such as Carboxy MethylCellulose (CMC) and Hydroxy Ethyl Cellulose (HEC), naturally occurringgums such as guar gum and xanthan gum, of the type of alkali swellableemulsions (ASE), such as aqueous acrylic copolymer dispersions, of thetype of hydrophobically modified alkali swellable emulsions (HASE).Thickeners are typically present in amounts ranging between 0.01 partand 1 part.

Other additives which can be present in the coating formulation of theinvention include dispersing agents, defoamers, insolubilisers orhardeners, dyes and optical brightening agents and/or biocides. Theseadditives are present in the coating formulation in quantum satis.

For example, the coating composition comprises 100 parts pigment, 2 to20 parts HBS, 0-10 parts of another type of modified starch, for exampleoxidized potato starch (Perfectacote), and 0 to 8 parts styrene-basedemulsion polymer binder, wherein the pigment is calcium carbonate. Inanother example, the coating formulation contains 100 parts pigment, 5to 20; or 5 to 15 parts; binder in which HBS comprises at least 50% ofthe total binder, preferably at least 60%, more preferably 70%, andwherein the pigment is calcium carbonate.

A coating formulation is readily prepared by standard methods. Pigmentsare typically added as slurry with solids contents between 25% and 78%,and HBS generally as solution with solids content between 25% and 60%,preferably about 50%. The pH of the coating formulation can be adjusted,e.g. within the range of pH 8.0-10.0 using a suitable base such asdiluted NaOH. A coating formulation of the invention is characterized bya number of unique properties. First, it shows an excellent stabilityand very low viscosity at elevated temperatures (e.g. 50° C.) whencompared to other starch-based coatings, like those containing oxidisedstarch or cold water soluble dextrin. In one embodiment, the coatingformulation has a Brookfield viscosity (RVDVII, 100 rpm, 25° C.) between100 and 2000 mPas, preferably between 200 and 1500 mPas, more preferablybetween 200 and 1200 mPas. The medium viscosity (Hercules High-shear1000 rpm, 25° C.) is typically below 400 mPas, preferably below 300mPas, more preferably below 250 mPas. The capillary viscosity (1*10exp6/s) is preferably below 100, more preferably below 80, morepreferably below 70 mPas.

Second, a coating formulation showed unexpectedly improved waterretention behaviour. For film coating application, fast immobilisationof the coating composition in the nip is of importance to avoid filmsplitting and subsequent misting. To this end, coating compositions withfast immobilisation speeds values are preferred. Increasing the starchamount in coating compositions usually has the opposite effect: theydecrease the immobilisation speed of the coating composition due to anincrease of the water retention behaviour, as the carbohydrate is astrong water binder. Surprisingly however, a coating composition withHBS shows a much lower water retention compared to coating compositionswith traditional coating starches and is therefore preferred for use infilm application.

Also provided is a coated paper comprising a paper and on the paper anamount of paper coating composition according to the present inventionfrom which the water has been reduced or removed. The coated paper ispreferably obtainable or obtained by a method of the invention. Thecoated paper is characterized by an increased paper surface strengthand/or increased paper brightness.

Still a further embodiment of the invention relates to the use of acoating formulation as disclosed herein in a process for film coating ofpaper or paperboard. Also provided is the use of a highly branchedstarch (HBS) having a molecular branching degree of at least 6% andwhich is obtained by treatment of starch or starch derivatives with aglycogen branching enzyme (EC 2.4.1.18) to improve the performance of afilm coating process or a film coater apparatus. As described hereinabove, improving performance comprises reducing misting, reducing waterretention, increasing paper surface strength, increasing paperbrightness, improving runnability, increasing immobilization speed, orany combination thereof.

The invention is further explained in and by the following ExperimentalSection

EXPERIMENTAL SECTION Materials and Methods

The BE used was the product NS28067 of Novozymes, a pilot plant productcontaining BE of Rhodothermus obamensis.

The Highly Branched Starch (HBS) was produced by jet cooking a 17% drysolid potato starch slurry (145-153° C., 8 min residence time, pressure4 bar) and after cooling down to 70° C. and adjusting the pH to 6.1,1000 units of enzyme (measured as the change in the absorbance of aiodine/iodide starch complex at 660 nm) were added per gram drysubstance of starch. After 20 h of incubation the enzyme was inactivatedby lowering the pH to 2.5 with 4M HCl and after 35 min the pH wasreadjusted to 4.5. Then the solution was filtered over a filter withpore size of 2-4 micrometer, followed by ion-exchange (Aquadem E200,Kruger). Finally, the solution was dried by evaporation of the waterfirst at 61° C. and then at 200° C. (temp out 82° C.). The activity ofthe enzyme is determined by monitoring changes in theiodine/iodide/amylose complex as a result of the branching enzymeactivity. A substrate solution is prepared by adding 10 mg Amylose typeIII (Sigma) to 0.5 ml 2 M NaOH, subsequently adding 1 ml ultra purewater and then adjusting the pH by adding 0.5 ml 2 M HCl and 7.8 mlphosphate buffer (pH 7.2). A iodine/iodide stock solution is prepared byadding 0.26 g 12 and 2.6 g KI to 10 ml ultra pure water. To 100microliter of this stock solution 50 microliter 2 M HCl is added and 26ml ultra pure water (stop reagent). The activity of the enzyme isdetermined by mixing 50 microliter of appropriately diluted enzyme to 50microliter of amylose substrate solution and incubating this for 30 minat 60° C. Then 2 ml of stop reagent is added and after mixing well theabsorbance is measured at 660 nm (the absorbance should be between 0.15and 0.3). The activity (U/mL) is calculated using the following formula:

U/ml=(OD _(reference) −OD _(sample))×100%×dilution/(OD _(reference) −OD_(blank))/30 min/0.05 ml

Analysis of Degree of Branching

The samples were suspended/solubilized in cold water in a closed tube.In order to reach complete gelatinization all samples were heated, underontinuous mixing, at 100° C. for 60 minutes. After cooling, acetatebuffer was added to set the pH to 3.8. The samples were debranched byovernight incubation with a high dosage of the enzyme isoamylase (fromPseudomonas sp.) at 35° C. Finally, for chain length distributionanalysis the samples were stabilized by addition of 9 volumes of DMSO.For the degree of branching assay the total carbohydrate was determinedby the anthrone method (gives total glucose) and a Luff-Schoorltitration (gives total reducing glucose end groups) was done. Thequotient of the two values (Luff/anthrone×100%).

Starch Derivatives:

Perfectacote 35 (P35): low viscous oxidised potato starch from AVEBEPerfectacote 45 (P45): low viscous oxidised potato starch from AVEBEPerfectacote 55 (P55): medium viscous oxidised potato starch from AVEBEC*Icote: cold water soluble starch from CargillHBS: Highly branched starch, prepared as described above

Pigments

Hydrocarb 75 is a ground calcium carbonate and was obtained from Omya AGand used as a slurry with dry solids content of 78%. Hydrocarb 60 wasobtained from Omya AG and used as a slurry with dry solids content of78.4%. Capim DG is a Kaolin obtained from Imerys and used as a slurrywith dry solids content of 70.5%.

Latex

Following types of lattices were used to prepare different coatingcompositions:

EOC L607 is a Styrene-Butadiene co-polymer latex from EOC (Belgium).Styronal D517 is a Styrene-Butadiene copolymer latex from BASF.Basonal 2119.02 is a Styrene-n-butyl acrylate copolymer latex from BASF.

Additives for Coating

Sterocoll FS is a synthetic thickener from BASF.

Dissolution of Starch in Hot Water

Starch is added in cold water in a tank, equipped with a suitablestirrer. The obtained starch slurry is then heated in a water bath withwell-dispersed live steam to a temperature of 95° C. This temperaturewas maintained for 20 minutes. The starch solution is stored at 50° C.before use.

Cold Water Solubility

Starch is added to water of 20° C. in a 1 L beaker to make 600 g totalweight, while stirring with an 8-holes stirrer at 600 rpm. The stirringis continued for 30 minutes. A precisely known amount of the starchsolution is sieved over 75 μm sieve. The residue from the sievetransferred quantitatively to an aluminum cup and dried in an oven at105° C. From the dry weight, the amount of non-dissolving starch can becalculated as a percentage. The Cold water solubility is expressed as100%-non-dissolving part %.

Brookfield Viscosity of a Starch Solution

Starch viscosity is measured in a 300 mL glass beaker with a Brookfieldtype LVF at 60 rpm and 50° C. using the appropriate spindle. The valueis recorded when the viscosity is stable or after 60 s.

Colour of a Starch Solution with Helliger Tester

For this test a Hellige Neo-Komparator is used with glass cuvettes of 13mm length. Fill the cuvette with the starch solution. Mount the mostsuitable Gardner Colour Disc into the apparatus. Turn the disc until thecolour in left part equals that of the right part. Read the colournumber from the Gardner Colour disc.

Preparation of a Coating Formulation

Add the pigment slurry (1000 g dry) into a 2000 mL beaker and dispersewith a dilutor. Add water if necessary. Add starch (dry if cold watersoluble) or a starch solution while stirring. Add synthetic binders tothe dispersion while stirring. Finally, add other additives to thecoating formulation. Adjust the formulation to the required pH withdiluted sodium hydroxide solution (16 w/w %). Adjust the temperature ofthe coating formulation au bain Marie. Dilute the coating compositionwith water to the required dry solids.

Coating Formulation Rheology.

Brookfield viscosity: Brookfield RVDVII, 100 rpm, 25° C. The coating ismeasured in the 500 mL beaker.

Medium viscosity: Hercules DV-10 High-shear at 100 and 1000 rpm, 25° C.

Bob/cup method is used, using Bob type A.

High shear viscosity: ACAV A2 Ultra High Shear capilary viscometer at1*10⁶ s⁻¹.

Water Retention: ÅA-GWR

Cover a filter paper (Whatman Cat. No. 1442-070) with a polycarbonatemembrane (5.0 μm, Ankersmit, art. Nr. 13068) and place a cylinder on topof it. Meter 8 mL of coating formulation into the cylinder and close thecylinder. Bring it to pressure of 1.5 bar with air for 15 seconds. Weighthe filter paper to record the weight increase and calculate it intog/m². The water retention is expressed as the amount of water that ispressed out of the liquid coating formulation. Hence, a lower valueindicates a stronger water retention.

Dry Solids

Dry solid content of coating formulations is measured with a CEM Labwave9000 at 100% power.

Paper Testing

All papers are conditioned at 23° C. and 50% moisture for at least threedays prior to paper testing.

Bending Stiffness

Bending stiffness is measured according to ISO-2493, using test stripsof 38 mm width, bending to an angle of 15°, with a free length of 10 mm.The maximum force of resistance is recorded and expressed in mN. Fivesamples in machine direction (MD) and five in cross direction (CD) aremeasured.

Dry Pick Resistance

Dry pick resistance is measured according to NEN-ISO-3783, using an IGTpick testes type AIC 2-5. The test is run with 8 μm oil thickness on 1cm disks, using a middle viscous IGT oil at a speed of 5 m/s. The pointwhere the pick resistance starts is multiplied with the viscosity of theoil (520) and expressed as VVP (viscosity velocity product).

Wet Pick/Ink Transfer

Ink transfer and wet pick resistance are measured using a Prüfbauprintability tester. Paper samples (47 mm×230 mm) are mounted on teststrips. 200 mm³ ink (Huber no. 408002) is applied to the rubber inkingreel which is equally distributes the ink during 30 s. Then the ink istransferred during 15 s to an ink-roll. 15 mm³ of off-set water (86%demi-water, 10% iso-propanol, 4% combimat.) is added to the moisteningstation. The ink-roll is mounted to the print station. The paper sampleis first (partly) wetted with the off-set water and immediately afterprinted with the ink-roll at a speed of 1 m/s. The sample is dried atthe air. The ink density of the moistened part (a) as well as of thenon-moistened part (b) of the paper test strip is measured using adensitometer. This gives the Ink transfer (a/b*100%) or Wet pick(100%-Ink transfer).

Example 1 Stability of the Coating Formulation

This Example shows the excellent stability at high concentrations of HBSin comparison with other coating starches. For stability and colourmeasurements, starches were dissolved in hot water. The cold watersolubility was determined as described above.

The HBS solution at a solids content of 50% or 35% is very stable with avery low viscosity at 50° C. when compared to the other componentstested. Except for the HBS solution that was very clear, colourless andtransparent, all solutions were yellowish to brown.

TABLE 1 Brookfield viscosity (mPas) in time at 50° C. HBS HBS CWS P35P55 Time (h) 50% 35% dextrin 35% 35% 35% 0 488 42  830 195 620 1 610 441260 220 780 2 580 44 1340 220 790 4 620 45 1400 215 810 24 580 44 1300270 1210 Colour (1 h) <1 <1   8 4 3 Cold water >99.9% >99.9%    50% Cookup Cook up Solubility starch starch CWS = Cold Water Soluble dextrin(=C*Icoat from Cargill)

Example 2 Rheology

This Example illustrates the excellent rheology characteristics that HBSgives to a coating composition for film coating application, as solebinder, but also in combination with SB latex. The example also showsthat the coating composition as prepared according to Example 2 ofEP060170B2 does not have favourable rheology characteristics forapplication in a film coater. Coating compositions for film coatingapplication were prepared using HBS and tested on rheology behaviour. Atleast 50% of the binder is comprised of starch.

Reference coating 1 (R1) is a coating composition comprising 100 partscalcium carbonate pigment, 7.5 parts Perfectacote 45 and 7 parts latex.

Reference coating 2 (R2) is a coating composition comprising 100 partsKaolin pigment (SPS Clay) and 12.5 parts HBS, according to EP0690170B2.

Coating 1 (C1) of the invention is a coating composition comprising 100parts calcium carbonate pigment, 7.5 parts HBS and 7 parts latex.

Coating 2 (C2) of the invention is coating composition comprising 100parts calcium carbonate pigment and 14.5 parts HBS as the sole binder.

TABLE 2 Solids content R1 R2 C1 C2 Coating composition Hydrocarb 75 78%100 100 100 SPS Clay 68% 100 Latex EOC L607 50% 7 7 Perfectacote 45 33%7.5 HBS 50% 12.5 7.5 14.5 Analysis Dry solids [%] 66 70.3 69 67 pH 9.59.5 9.5 9.5 Brookfield 100 rpm mPas 700 4680 360 408 Hercules High shearmPas 122 >> * 57 206 1000 rpm @25° C. ACAV visco. @1*10⁶ s⁻¹, mPas49 >> * 50 64 25° C. AAGWR @ 1.5 bar, 15 sec g/m² 19 17.5 40 12 * Theviscosity of the Reference coating composition R2 is too high formeasuring the Rotational high shear viscosity at 1000 rpm or thecapillary viscosity (ACAV) at 70.3% solids as mentioned in EP0690170B2.

Due to its low viscosity at high concentrations, HBS can be used toincrease the dry solid content of a coating considerably. Compare R1with C1, where an increase of 3% can be achieved without increasing thehigh shear reology. In combination with the water retention propertiesit gives to the coating composition, makes HBS suitable to use as starchbinder in a coating composition in a film coater at high solidconcentration. In contrast, the coating composition containing HBSaccording to Example 2 of EP0690170B2 is not suitable for film coatingapplication.

Table 2 shows that the High shear viscosity of Reference coating R2 isso high that viscosity could not be measured with Rotational viscometer(Hercules) nor with Capillary viscometry (ACAV). On the other hand, thecoating composition with only HBS as binder from the invention (C2)shows to have acceptable (ACAV <70 mPas) rheology properties for filmcoating application.

Example 2B Improved Water Retention Behaviour for Film Coating

TABLE 3 Coating compositions for film coating application d.s. Hydrocarb75 78% 100 100 100 100 P35 35% 8 P55 35% 8 HBS 35% 8 C*Icoat 35% 8Styronal DL517 50% 8 8 8 8 pH 9 9 9 9 Dry solids [%] 66 66 66 66 T [°C.] 25 25 25 25 Brkfld 100 rpm @ 25° C. [mPas] 660 1240 100 208 Waterretention [g/m²] 21 9 64 26

Table 3 shows that a coating composition with HBS shows a lower waterretention (higher value) compared to other coating starches in coatingcompositions with the same starch content, dry solids and temperature,which is better for application in film press.

Example 3 Coated Paper to Evaluate Binding Power of HBS

This example shows that HBS as binder can be applied at high dry solidsin increasing HBS/Latex ratios, while maintaining the same surfacestrength. Various coating compositions were prepared (see Table 4). Thecoating composition was applied onto 80 gsm woodfree basepaper fromBurgo Ardennes using the puddle type blade from the Dixon coater at aspeed of 50 m/min. Approximately 10 gsm of coating was applied.Sterocoll FS was added in order to adjust the Brookfield viscosity ifnecessary. The paper was dried to a moisture content of 5%. Before papertesting the papers were conditioned at 23° C. and 50% relative humidity.As is clear from Table 4, the formulations with HBS yielded a highersurface strength compared to a formulation with a regular low viscousstarch (Perfectacote 35).

TABLE 4 d.s. A B C D E F Hydrocarb 75 78% 100 100 100 100 100 100Perfectacote 55 35% 6 Perfectacote 35 35% 6 HBS 50% 6 8 10 12 LatexDL517 50% 6 6 6 4 2 0 Sterocoll FS Asis 0.3 0.25 0.2 0.2 pH 9 9 9 9 9 9Water q.s. Dry solids [%] 65.1 68.3 68.0 67.9 68.1 68.1 Brookfield 100rpm [mPas] 740 503 800 680 520 540 Coatweight [gsm] 9.7 9.9 9.8 9.8 9.89.9 IGT dry pick [VVP] 610 503 551 526 540 529

Example 4 Use of Coating Formulations in Film Coating

This example shows that the application of the coating compositionsaccording to the invention (C1 and C2 from Example 2) via film coatingoperation onto a paper web results in higher dry solids, improvedrunnability and improved paper properties in comparison with thereference coating compositions R1 and R2.

Coating compositions R1, R2, C1, C2 (see Example 2) were applied onto 66gsm fine base paper (Burgo Ardennes) using a pre-metered size film presscoater (Optisizer) at a speed of 1300 m/min applying 13 gsm/side using25 mm smooth rod. The paper was dried to 4% moisture. The paper sampleswere conditioned and tested at 23° C. and 50% relative humidity. Table 5shows the runnability as well as the quality of the single coated paperproduced with the pre-metered film press coater.

Although R2 could be prepared at high solids, it had to be diluted togive acceptable runnability on the film coater. Therefore, the coatingcomposition was diluted to 61.9% solids on machine until acceptable rodpressure was achieved and the targeted coat weight could be applied.However, due to the low solids, the coating gave severe misting.

TABLE 5 Single coated paper by film coating Dry solids R1 R2 C1 C2Coating composition Hydrocarb 75 78 100 100 100 SPS Clay    68% 100Latex EOC L607 50 7 7 Perfectacote 45 33 7.5 HBS 50 12.5 7.5 14.5Analysis Dry solids [%] 66.4 61.9 69.4 67.4 pH 9.4 9.3 9.2 9.3Brookfield 100 mPas 803 330 413 263 Machine data Coat weight Gsm 26 2626 26 Speed m/min 1305 1305 1305 1305 Rod pressure Bar 2.1 2.4 2.0 2.3Misting (0-5) 3 5 2 0 Paper testing Bending MD mN 109 115 101 128Bending CD mN 57 56 49 62 IGT dry pick c.s. VVP 1560 1460 1400 1660 IGTdry pick u.s. VVP 1210 1300 1200 1470 Prüfbau ink transf % 100 87 98.989 [%] Wet pick [%] % 0 12 1.1 11

Example 5 Exemplary Coating Formulations

TABLE 6 Coating formulations according to the invention 1 2 3 4Hydrocarb 60 85 Hydrocarb 75 15 70 80 90 Capim DG 30 20 10 HBS 6 7 7 7Basonal 2119.02 6 Styronal DL 517 5 5 5 Sterocoll SL 0.15 FinFix 5 0.15Dry solids (%) 72 70.0 69.9 70.2 Brkfld 100 rpm @ 25° C. 1070 330 236220 Hercules High shear 205 140 106 107 1000 rpm @25° C. Water retention56 69 75 76

1. A method for preparing coated paper comprising the steps of: a)providing a pigmented wet coating formulation comprising water, 2-20parts of a binder and 100 parts of pigment, wherein at least 50% of thebinder is highly branched starch (HBS) characterized by a molecularweight of between 0.5*105 and 1*106 Daltons and having a molecularbranching degree of at least 6% and which is obtained by treatment ofgelatinized starch or starch derivative with a glycogen branching enzyme(EC 2.4.1.18); and wherein at least 70% of the pigment is calciumcarbonate; and b) applying the pigmented wet coating formulation topaper by film coating and drying the coated paper.
 2. The methodaccording to claim 1, wherein the HBS has a molecular weight between0.8*10⁵ g/mol to 1.8*10⁵ g/mol, preferably between 1*10⁵ g/mol and1.6*10⁵ g/mol.
 3. The method according to claim 1, wherein the HBS doesnot contain any residual amylose.
 4. The method according to claim 1,wherein at least 70% of the binder is HBS and wherein at least 80% ofthe pigment is calcium carbonate.
 5. The method according to claim 1,wherein said starch or starch derivative is selected from native,unmodified and chemically modified starch derived from non-GMO as wellas GMO plant variants.
 6. Method according to claim 5, wherein thestarch or starch derivative is derived from potato, corn, wheat,tapioca, waxy potato, waxy corn, waxy tapioca, like high amylose potato,high amylose corn, and modified starches including low DE maltodextrinsand amylomaltase-treated starch.
 7. The method according to claim 5,wherein the starch derivatives are selected from the group consisting ofthe products of acid or enzymatic hydrolysis of starch and the productsof the chemical and physical modifications of starch of any type.
 8. Themethod according to claim 7, wherein starch derivative is cationicstarch, oxidized starch or phosphated starch.
 9. The method according toclaim 1, wherein said glycogen branching enzyme is a thermostableglycogen branching enzyme obtained from a mesophilic or thermophilicorganism, preferably glycogen branching enzyme of Aquifex aeolicus orRhodothermus obamensis.
 10. The method according to claim 1, wherein HBSis the sole binder.
 11. The method according to claim 1, wherein thepigmented wet coating formulation comprises 100 parts pigment, 2 to 20parts HBS, 0-10 parts of another modified starch, and 0 to 8 partsstyrene-based emulsion polymer binder, and wherein the pigment iscalcium carbonate.
 12. The method according to claim 1, wherein thesolids content of the wet coating formulation is at least 60% by weight,preferably at least 65%, more preferably at least 70% by weight.
 13. Themethod according to claim 1, wherein step b) comprises applying thecoating formulation at a speed of at least 1200 m/min in an amount of atleast 7 gsm/side by film coating.
 14. A pigmented wet paper coatingcomposition comprising water, 2-20 parts of a binder and 100 parts ofpigment, wherein at least 50% of the binder is highly branched starch(HBS) characterized by a molecular weight of between 0.5*10⁵ and 1*10⁶Daltons and having a molecular branching degree of at least 6% and whichis obtained by treatment of starch or starch derivatives with a glycogenbranching enzyme (EC 2.4.1.18); and wherein at least 70% of the pigmentis calcium carbonate.
 15. The coating composition according to claim 14,having a dry solids content of at least 65% by weight, comprising atleast 80% by weight calcium carbonate as its pigment component and amodified starch as binder, the modified starch consisting of said highlybranched starch (HBS).
 16. The coating composition according to claim14, wherein said HBS has a molecular weight between 0.8*10⁵ g/mol to1.8*10⁵ g/mol, preferably between 1*10⁵ g/mol and 1.6*10⁵ g/mol.
 17. Thecoating composition according to claim 14, wherein the HBS does notcontain any residual amylose, preferably measured. according to theKI/I₂ test.
 18. Coating composition according to claim 14, comprising100 parts pigment, 2 to 20 parts HBS, 0-10 parts of another modifiedstarch, and 0 to 8 parts styrene-based emulsion polymer binder, andwherein the pigment is calcium carbonate.
 19. Coating compositionaccording to claim 14, comprising 100 parts pigment, 5 to 20 partsbinder in which HBS comprises at least 50%, preferably at least 60%,more preferably 70%, of the total binder and in which said pigment iscalcium carbonate.
 20. A coated paper comprising a paper and on thepaper an amount of paper coating composition according to claim 14 fromwhich the water has been reduced or removed.
 21. Coating compositionaccording to claim 14 for use in film coating of paper or paperboard.22. The use of a highly branched starch (HBS) characterized by amolecular weight of between 0.5*10⁵ and 1*10⁶ Daltons and having amolecular branching degree of at least 6% and which is obtained bytreatment of starch or starch derivatives with a glycogen branchingenzyme (EC 2.4.1.18) to improve the performance of a film coatingprocess or a film coater apparatus.
 23. Use according to claim 22,wherein improving performance comprises reducing misting, reducing waterretention, increasing paper surface strength, increasing paperbrightness, improving runnability, increasing immobilization speed, orany combination thereof.